Alkaline cyanide zinc electroplating

ABSTRACT

AQUEOUS, ALKALINE CYANIDE ZINC ELECTROPLATING BATHS AND PROCESSES ARE PROVIDED WHICH ELECTRODEPOSIT BRIGHT ZINC AT LOW CYANIDE CONCENTRATIONS BY USING AS AN ADDITION AGENT A COMBINATION OF POLYETHYLENIMINE HAVING A MOLECULAR WEIGHT BETWEEN ABOUT 600 AND 60,000 AND A QUATERNARY PYRIDINE COMPOUND OF THE FORMULA:   1-R,3-((-)OOC-)PYRIDINIUM   WHEREIN R IS ALKYL, ALKENYL OR ALKYNYL OF 1 TO 4 CARBON ATOMS, BENZYL AND SUBSTITUTED BENZYL WHEREIN THE SUBSTITUTENT IS AT LEAST ONE OF ALKYL OF 1 TO 4 CARBON ATOMS, HALOGEN, CYANIDE, ALKOXY OF 1 TO 4 CARBON ATOMS, PHENYL AND   1-((-)CH2-),3-((-)OOC-)PYRIDINIUM   OR A HYDROHALIDE SALT THEREOF, THE WEIGHT RATIO OF POLYETHYLENIMINE TO QUATERNARY PYRIDINE COMPOUND BEING WITHIN THE RANGE OF 10:1 TO 1:100. THE ELECTROPLATING BATH HAS A WEIGHT RATIO OF CYANIDE TO ZINC WITHIN THE RANGE OF 0.1-3.5:1, PREFERABLY ABOUT 1:1.

United States Patent O U.s. Cl. 204-55 Y 18 Claims ABSTRACT OF THE DISCLOSURE Aqueous, alkaline cyanide zinc electroplating baths and processes are provided which electrodeposit bright zinc at low cyanide concentrations by using as an addition agent a combination of polyethylenimine having a molecular weight between about 600 and 60,000 and a quaternary pyridine compound of the formula:

COO-

wherein R is alkyl, alkenyl or alkynyl of 1 to 4 carbon atoms, benzyl and substituted benzyl wherein the substituent is at least one of alkyl of 1 to 4 carbon atoms, halogen, cyanide, alkoxy of 1 to 4 carbon atoms, phenyl and or a hydrohalide salt thereof,

the weight ratio of polyethylenimine to quaternary pyridine compound being within the range of :1 to 1:100. The electroplating bath has a weight ratio of cyanide to zinc within the range of 0.1-3.5: 1, preferably about 1:1.

BACKGROUND OF THE INVENTION Field of invention This invention relates to zinc electroplating baths and processes and more particularly to alkaline, cyamde zinc electroplating baths and processes.

Prior art Most of the zinc electroplating today is carried out from alkaline cyanide baths having high cyanide concentrations, i.e., greater than about 35 grams per liter. Many materials have been disclosed in the art for use as brighteners in these baths, including aldehydes, polyvinyl alcohols, polyethylenimines (US. Pat. 3,393,135) and quaternary nitrogen compounds (U.S. Pats. 3,318,787 and 3,411,996).

There are occasions when it is desired to electroplate zinc at lower cyanide concentrations. While the aldehyde brighteners are effective at these lower concentrations, they are unstable and necessitate frequent replenishment. On the other hand, the known permanent-type brighteners, i.e., the above polyvinyl alcohols, polyethylenimine and quaternary nitrogen compounds, do not give a fully bright zinc plate at the lower concentrations. Thus, there is a need in the art for a brightening system which will give a fully bright zinc plate at low cyanide levels and which can be used to make a running conversion from high cyanide levels to low cyanide levels without sacrificing zinc brightness.

3,734,839 Patented May 22, 1973 SUMMARY OF THE INVENTION wherein R is alkyl, alkenyl or alkynyl of 1 to 4 carbon atoms, benzyl and substituted benzyl wherein the substituent is at least one of alkyl of 1 to 4 carbon atoms, halogen, cyanide, alkoxy of 1 to 4 carbon atoms, phenyl and or a hydrohalide salt thereof,

the weight ratio of polyethylenimine to quaternary pyridine compound being within the range of 10:1 to 1:100 and said bath having a weight ratio of cyanide to zinc within the range of 0.1-3.5: 1.

There is also provided an improved zinc electroplating process which comprises electroplating zinc from the above-described bath.

There is further provided an aqueous addition agent for an alkaline electroplating bath consisting essentially of an aqueous solution at a pH between 4.5 and 8 of a combination of polyethylenimine having a molecular Weight between about 600 and 60,000 and a quaternary pyridine compound of the formula:

wherein R is alkyl, alkenyl or alkynyl of 1 to 4 carbon atoms, benzyl and substituted benzyl wherein the substituent is at least one of alkyl of 1 to 4 carbon atoms, halogen, cyanide, alkoxy of 1 to 4 carbon atoms, phenor a hydrohalide salt thereof,

the weight ratio of polyethylenimine to quaternary pyridine compound being within the range of 10:1 to 1:100, said combination being at a concentration in solution of between 1 and 50 percent by weight.

DETAILED DESCRIPTION OF THE INVENTION 3,734,339 r 3 4 u r The polyethylenimine useful in the plating bath has a erably at about 1 to 30 percent by weight. In order to molecular weight range of about 600 to 60,000. Molecular have an addition agent of prolonged shelf stabiilty, the weights below 600 and about 60,000 may also be empH of the aqueous solution should be between about 4.5 ployed, although those below 600 are not generally availand 8. At a pH outside this range the quaternary pyridine able commercially while those much over 60,000 are not 5 compound will tend to precipitate or the solution will be sufficiently soluble to be generally useful. Molecular unduly unstable. A preferred pH range is 5.5 to 7. weights between about 600 and 1800 are preferred. Poly- The plating bath is operated according to normal proethylenimine is added to the bath to give a concentration cedures using a sodium cyanide concentration within the of 0.005 to 2 grams per liter, preferably 0.02 to 0.2 gram range of about 5 to 45 grams per liter, preferably 5 to 20 per liter for barrel plating and 0.05 to 0.5 gram per liter grams per liter, and most preferably about 7 grams per for rack plating. liter and a zinc concentration of about 5 to 20 grams per The quaternary pyridine compounds useful in the liter, and most preferably about 7 grams per liter. As plating bath have the general formula: mentioned previously, the higher cyanide concentrations are employed in high cyanide plating baths and the present brightening system is effective at these concentrations to enable the electroplater to convert his bath to lower cyanide levels, i.e., in the range of about 5 to grams per liter. It has been found that the weight ratio of cyanide R to zinc should be in the range of about 0.1-3.5 :1, prefwherein R is alkyl, alkenyl, or alkynyl of 1 to 4 carbon 20 erably about 1:1 to 2:1 at the low cyanide levels. Plating atoms, benzyl and substituted benzyl wherein the ubbath temperatures will usually be between 20 and 40 C.,

stituent is at least one of alkyl of 1 to 4 carbon atoms, however, the brightening system can provide bright dehalogen, cyanide, alkoxy of 1 to 4 carbon atoms, phenyl posits over a wide current density range at temperatures and up 10 55 C- Other bath-soluble polymers may be added to the CHz-N plating bath in particular situations to give further improvements in operation. In particular, polyvinyl alcohol 00- or an oxidized polyvinyl alcohol can be used to replace or a hydrohalide salt ther of, a portion of the polyethylenimine in rack plating to give improved brightness to the zinc deposit. While Particularly Preferred compounds are y The brightening system of the present invention has the pyridinium 3-Carb0XYlat and y pyridinium advantages of good shelf life, good chemical stability in boxylate, other compounds which may be used are 1-(4- the plating bath and a wide operating range so that the methylbenlyl) pyridinium 3-cafboxylflte, 'M- electroplater can make a running conversion from a high y pyridinium 3-carb0Xy1ate, y pyridinium cyanide bath to a low cyanide bath without affecting the carboxylate, and l-propargyl pyridinium 3-carboxylate. uality of the plating work.

Thfise Compounds can also be Used as the hy r h l The invention can be further understood by referring salts such as hydrochloride or hydrobromide. The quatert th following examples in which parts and percentages nary pyridine compound is added to the bath to give are b weight unl other i indi t d,

a concentration of 0.005 to 10 grams per liter, pref- 40 erably 0.02 to 0.5 gram per liter. EXAMPLES 1 TO 8 When adding the polyethylenimine and quaternary pyridine compound to the plating bath, the weight ratio An q Stock electfoplatlng 5011111011 Was made of the former to the latter should be within the range having the following composition:

of 10:1 to 1:100, preferably about 1:1 to 1:20. The exact G A ratio used will depend upon the type of plating operation employed, the temperature of operation and the concen- Zn metaufmm Zno) tration of the bath. Generally, when the concentration of Sodium cyamdq the bath increases the Wei ht ratio will shift to hi her Sdmm hydmxlde 75 g g Sodium carbonate 52 concentrations of the quaternary pyridine compound.

The combination of brightening ingredients used are Hull Cell panels were plated at 25 C. for 5 minutes at preferably used in the form of aqueous addition agents for 2 amps. using combinations of polyethylenimine and a zinc electroplating baths. Additives for the plating baths quaternary pyridine compound as brighteners in the stock can be prepared by dissolving the polyethylenimine and 55 solution. Each panel was bright-dipped in dilute nitric quaternary pyridine compound at the desired ratio at a acid before examination. The brightener added and results solids content of about 1 to 50 percent by weight, prefare shown in Table I.

TABLE I Example No. Brlghtener added Panel appearance Control Nona Dull overall.

.2 g./l.PEI,M.W.1,200.. Do .2 g./l. PEI, M.W. 1,300

DullDabove 2.2 A./dm. semibrlght below 2.2 A.ldm..

Semi-bright from high current end to .2 AJdmJ; haze below .2 AJdmfl. Semi-bright from high current end to 4.3 A./dm. bright from 4.3 to .2

2 .20 g.ll. PEI, M.W. 600; .26 g./l. BPO Semi-bright high current end to 5.4 A.Idm. bright from 5.4 A./d m. to

.2 A./dm. haze below .2 AJdmfi.

3 .20 g.l1. PEI, M.W. 1,200; .26 g./l. BPC Semi-bright from high current end to 4.9 A./dm. bright from 4.9 A./dm.

to .3 A./dm. haze below .3 A./d m. .20 g./l. PEI, M.W. 1,200, .26 g./l. trlgonelllne hydrochloride. Semi-bright above 3.8 A.ldm. bright from 3.8 AJdm. to 1.3 A./dm.

heavy haze below 1.3 A./dm. 5 .2tingdll. PBIIII, M.W. 1,200, .26 g./l. 4'-methy1 BPC hydro- SergliffilifbOvo 3.8 A.ldm. bright 3.8 AJdm. to .2 AJdmfl; haze below 6 .20 g./l. PEI, M.W. 1,800; 4.0 gJl. BPC senilkbrgllllg above 6.5 A.ldm. bright below 6.5 A.ldm. slight haze below 7 1.1 g./l. PEI, M.W. 1,800; .26 g./l. BPO. se'lgiibrglllit above 11 A./dm. bright below 11 A.Idm. slight haze below 8 26.0 g./l. NaCN (total); .2 g.ll. PEI, M.W. 600, .26 g./l. BOP- Whole panel bright, very light light haze above 1.7 A.Idm.

h drNgrE.1$PO=1-benzy1pyridiniiun 3-carb0xylate; PEI=Polyethy1enimine; qnethyl BPC=l -(4,-methylbenzyl) pryidinium a-carbogylate y 0 tom 0.

EXAMPLE 9 Hull Cell panels were plated for 5 minutes at 2 amps. at 25 C., 35 C. and 45 C. from a plating bath of the following composition:

G./l. Zinc metal (from ZnO) 7.5 Sodium cyanide 15.0 Sodium bicarbonate 20 Sodium carbonate 132 l-benzyl pyridinium 3-carboxylate 1 Polyethylenimine M.W. 1200 1 The panel plated at 25 C. was bright overall with light haze above 2.6 a./dm. and dark haze below 2.6 a./dm. the panel plated at 35 C. was bright overall with the top 4 mm. of the panel dull and the panel plated at 45 C. was bright overall withlight haze below .1 aJdm.

EXAMPLE Screws barrel plated for minutes at 1.5 amps. at both C. and 35 C. were full bright when plated from a bath of the following composition:

G./l. Zinc metal (from ZnO) 7.4 Sodium cyanide 7.6 Sodium hydroxide 77 Sodium carbonate 62 Polyethylenimine--M.W. 1200 .43 l-benzyl pyridinium 3-carboxylate .43

EXAMPLE 1 l Screws barrel plated at 25 C. for 20 minutes at 1.5 amps. were liquid bright when plated from a bath of the following composition:

G./l. Z-inc metal (from ZnO) 7.5 Sodium cyanide 7.5 Sodium hydroxide 75 Sodium carbonate 52 Polyethylenimine-M.W. 1200 .047 l-benzyl pyridinium 3-carboxylate .047

What is claimed is:

1. In an aqueous alkaline cyanide zinc electroplating bath the improvement comprising: having added to said bath, in an amount eflective to yield a zinc deposit of improved brightness, a combination of polyethylenimine having a molecular weight between about 600 and 60,000 and a quaternary pyridine compound of the formula:

wherein R is alkyl, alkenyl or alkynyl of 1 to 4 carbon atoms, benzyl and substituted benzyl wherein the substituent is at least one of alkyl of 1 to 4 carbon atoms, halogen, cyanide, alkoxy of 1 to 4 carbon atoms, phenyl and war I about 600 and 1800 which is at a concentration within the range of 0.005 to 2 grams per liter.

3. The zinc electroplating bath of claim 1 wherein the quaternary pyridine compound is at a concentration within the range of 0.005 to 10 grams per liter.

4. The zinc electroplating bath of claim 1 wherein the quaternary pyridine compound is l-benzyl pyridinium 3- carboxylate.

5. The zinc electroplating bath of claim 1 wherein the ratio of polyethylenimine to quaternary pyridine compound is about 1:1 to about 1: 10.

6. The zinc electroplating bath of claim 1 wherein the ratio of cyanide to Zinc is about 1:1 to about 2: 1.

7. In an aqueous alkaline cyanide zinc electroplating bath the improvement comprising: having added to said bath a combination of polyethylenimine having a molecular weight within the range of about 600 and 1800 and l-benzyl pyridinium 3-carboxylate, at a weight ratio within the range of about 1:1 to 1:20 and each at a concentration within the range of about 0.02 to 0.5 gram per liter, said bath having a weight ratio of cyanide to zinc of 1:1 at a cyanide concentration as sodium cyanide of about 5 to 20 grams per liter.

8. In a process for electrodepositing zinc from an aque ous, alkaline cyanide electroplating bath, the improvement comprising: adding to said bath in an amount effective to yield a zinc deposit of improved brightness a combination of polyethylenimine having a molecular weight between about 600 and 60,000 and a quaternary pyridine compound of the formula:

wherein R is alkyl, alkenyl or alkynyl of 1 to 4 carbon atoms, benzyl and substituted benzyl wherein the substituent'is at least one of alkyl of 1 to 4 carbon atoms, halogen, cyanide, alkoxy of 1 to 4 carbon atoms,

or a hydrohalide salt thereof, the weight ratio of polyethylenimine to quaternary pyridine compound being within the range of 10:1 to 1:100, maintaining said bath at a weight ratio of cyanide to zinc within the range of 0.1-3.5 :1, and said polyethylenirnine being at a concentration within the range of 0.005 to 2 grams per liter.

9. The process of claim 8 wherein the polyethylenimine molecular weight is within the range of of about 600 to 1800 and wherein the polyethylenimine is added to give a concentration within the range of 0.005 to 2 grams per liter.

10. The process of claim 8 wherein the quaternary pyridine compound is added to give a concentration within the range of 0.005 to 10 grams per liter.

11. The process of claim 8 wherein the ratio of polyethylenimine to quaternary nitrogen compound is about 1:1 to about 1:10.

12. The process of claim 8 wherein the ratio of cyanide to zinc is about 1:1 to about 2: 1.

13. In a process for electrodepositing zinc from an aqueous, alkaline, cyanide electroplating bath, the improvement comprising: electroplating zinc from the electroplating bath of claim 7.

14. An aqueous addition agent for an alkaline electroplating bath consisting essentially of an aqueous solution at a pH between 4.5 and 8 of a combination of polyethylenimine having a molecular weight between about 600 and 60,000 and a quaternary pyridine compound of the formula:

COO-

wherein R is alkyl, alkenyl or alkynyl of 1 to 4 carbon atoms, benzyl and substituted benzyl wherein the substituent is at least one of alkyl of 1 to 4 carbon atoms, halogen, cyanide, alkoxy of 1 to 4 carbon atoms, phenyl and COO- 15. The aqueous addition agent of claim 14 wherein the solution is at a pH between 5.5 and 7.

16. The aqueous addition agent of claim 15 wherein the polyethylenimine molecular weight is within the range of about 600 and 1800.

17. The aqueous addition agent of claim 16 wherein the quaternary pyridine compound is l-benzyl pyridinium 3-carboxylate.

18. The aqueous addition agent of claim 17 wherein the ratio of polyethylenimine to l-benzyl pyridinium 3- carboxylate is within the range of about 1: to 1:20.

References Cited UNITED STATES PATENTS 3,318,787 5/1967 Rindt et a1. 204-55 Y 3,411,996 11/19'68 Rushmore 204-55 Y X 3,472,743 10/ 1969 Rushmore 20455 Y FREDERICK C. EDMUNDSON, Primary Examiner U.S. Cl. X.R. 204Dig 2 UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION.

Patent No. 'll'3 I '839 Dated May 22, 1213 Inventor) P aul'Jean Hoyer aIId J oh n Derek Rushmere It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shownbelow:

Column 6, line 45, CH should read Q -CH -N coo- Column 8,',l ine 11; "1:" should read 1= 1--.'

Signed and sealed this 5th day of March 197M.

(SEAL) Attest:

EDWAR M FLE TQ HER, R. c. MARSHALL. DANN Attestlng fJ-Q Commissioner of Patents 

